The North Atlantic Ocean is characterized by an intense meridional circulation cell carrying near-surface waters of tropical and subtropical origin northward and deep waters of arctic and subarctic origin southward. The related "overturning" is driven by the sinking of water ... masses at high latitudes. The overturning rate and thus the intensity of the meridional transports of mass, heat, and salt, is an important control parameter for the modeling of the ocean's role in climate. Certainly such estimates require more than one survey of the study area; therefore, the Research Vessel (R/V) Meteor Cruise 18/1 was one in a series of cruises in the North Atlantic that started in March 1991 and continued until 1995.

This data documentation discusses the procedures and methods used to measure total carbon dioxide (TCO2) and total alkalinity (TALK) at hydrographic stations, as well as underway partial pressure of CO2 (pCO2) measured during the R/V Meteor Cruise 18/1 in the North Atlantic Ocean (Section A1E). Conducted as part of the World Ocean Circulation Experiment (WOCE) and the German North Atlantic Overturning Rate Determination expedition, the cruise began in Reykjavik, Iceland, on September 2, 1991, and ended after 24 days at sea in Hamburg, Germany, on September 25. 1991. WOCE Zonal Section A1E began at 60 N and 30(deg)30' W (southeast of Greenland) and continued southeast with a closely spaced series of hydrocasts to 52(deg)20' N and 14(deg)15' W (Porcupine Shelves). Measurements made along WOCE Section A1E included pressure, temperature, salinity, and oxygen measured by a conductivity, temperature and depth (CTD) sensor; bottle salinity; oxygen; phosphate; nitrate; nitrite; silicate; TCO2; TALK; and underway pCO2. A total of 61 CTD casts were made, including 59 bottle casts and 2 calibration stations. Replicate samples from seven Niskin bottles at five stations were also collected for later shoree-based reference analyses of TCO2 by vacuum extraction and manometry and TALK in the laboratory of Dr. Charles D. Keeling, Scripps Institution of Oceanography; these results are also included in this report.

TCO2 was measured by using an automated sample processsor, to extract CO2 from seawater samples, coupled to a coulometer, to detect the extracted gas. The precision and accuracy of the system was 11.60 umol/kg. Samples collected for TALK were measured using standard potentiometric techniques; precision was 12.0 umol.kg. Underway pCO2 was measured by infrared photometry; precision was 12 uatm.

The R/V Meteor Cruise 18/1 data set is available freee of charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center. The NDP consists of three oceanographic data files, three FORTRAN 77 data retrieval routine files, an readme file, and this printed documentation, which describes the contents and format of all files as well as the procedures and methods used to obtain the data.

Quality
An important part of the NDP process at the Carbon Dioxide Information Analysis Center (CDIAC) involves the quality assurance (QA) of data before distribution. Data received at CDIAC are rarely in a condition that would permit immediate distribution, regardless of the source. To guarantee data of the ... highest possible quality, CDIAC conducts extensive QA reviews that involve examining the data for completeness, reasonableness, and accuracy. Although they have common objectives, these reviews are tailored to each data set, often requiring extensive programming efforts. In short, the QA process is a critical component in the value-added concept of supplying accurate, usable data.